As is known, in order to detect an intrusion into, or out of, a protected volumetric space, a sensor sheet is provided to enclose the volume of interest which has a continuous electrical or optical signal path disposed in the sheet and substantially encompassing the full extent thereof. An electrical signal, in the case of a wire path, or an optical signal, in the case of an optical fiber path, is introduced to one end of the signal path, and the signal is received at the opposite end of the signal path. The presence of a signal indicates a normal or non-alarm state. In the event of a break or other interruption in the signal path, the loss or diminution of the signal is detected and signifies an alarm condition. In the case of an optical fiber signal path, the optical fiber can be sensitive to incident nuclear radiation that causes a reduction in the amplitude and/or characteristics of the optical signal and which can be detected as an indication of an alarm condition.
Current fabrication techniques for installation of sensor sheets involve first applying a resin layer to the surface of the object to be enclosed, e.g., the interior walls of a cargo container or the outer surface of a pipeline. The resin must be allowed to dry to a certain point and then, within a specified time window, i.e., before the resin hardens, the sensor sheet is to be laid on top. A top layer of resin is thereafter applied and allowed to dry to hold fast the sensor sheet in a protective sandwich construction.
A sensor security detector tape is described in U.S. Pat. No. 8,653,971 which includes a material strip with predetermined width and length and first and second ends. At least one signal path is provided in the material strip where each signal path has a first end and a second end. First and second connectors are coupled to the first and second ends, respectively, of the signal paths. The signal path may be either an electrical wire or an optical fiber.
In another embodiment, a sensor security detector tape includes a material strip having a predetermined width and a predetermined length and first and second ends and a plurality of signal paths where each signal path has a first end and a second end. First and second connectors are coupled to the first and second ends, respectively, of the signal paths.
In another embodiment, a plurality of conductive paths are connected at one end to a multiplexing circuit to which an input signal is applied for propagation along all of the conductive paths. The other end of the plurality of conductive paths is connected to a logical circuit which provides an output signal. A break in any one of the plurality of conductive paths will cause a loss of conduction in the broken paths and a change in the output signal from the logical circuit. The logical circuit in one implementation is an AND gate. The gate output is in one state when all of the conductive paths are intact and carrying a signal. The output of the gate will change state in the absence of conduction in any one or more of the paths. This change of state is indicative of an alarm condition. The logical circuit can be of other forms known to those of skill in the art to provide the intended function. The multiplexer and the AND gate or other logical circuit can be housed within respective connectors to which the plurality of signal paths are coupled.